PRELIMINARY CRYSTALLIZATION OF A CYCLIN-DEPENDENT KINASE INHIBITOR: P18. Shannon Jarchow and Hengming Ke

Department of Biochemistry and Biophysics, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA

Eukaryotic cell-cycle progression is regulated by a family of serine/threonine protein kinases, cyclin-dependent kinases (CDK's). CDK activity is regulated by subunit phosphorylation, activation via cyclin binding, and inhibition via binding of small regulatory proteins. Currently, these small inhibitor proteins can be classified into two families: the universal inhibitors of the p21/p27 family and the more specific inhibitors p16INK4 (p16)/p14INK4 (p14) family. A member of the p16/p14 family, p18 binds and inhibits CDK6 and CDK4, halting cell cycle progression.

Recombinant human p18 has been purified to homogeneity and diffraction quality crystals have been obtained by dialysis. Crystals have a typical size of 0.1 x 0.1 x 0.2 mm and can diffract to 2Å resolution. The space group has been determined to be P1 with unit cell dimensions of: a=60.3, b=40.2, c=28.4 Å, (=90.6deg., ß=92.1deg., (=95.8deg.. Diffraction data have been collected on a RIGAKU R-AXIS image phosphate system. A data set of 16,785 measurements has been reduced to 11,595 independent reflection with an R-merge of 0.089. This data set is 70.5% complete to 2.06Å resolution. Heavy atom derivative preparation and structural analysis is in progress.